New test proposed to determine origin of biodiesel feedstock

By Ehsan Ali | February 27, 2015

Biodiesel has become an important, global renewable fuel that can be produced from different edible or nonedible feedstock. Biofuel or biodiesel production from edible crops may be subject to the mounting food-vs.-fuel and indirect land use change debates. As biodiesel is an emerging market and growing quickly, production of oil for biodiesel will continue to be a profitable business. The popularity of biodiesel may create some future conflicts while assessing the source of oil as edible or nonedible and expected shelf life depending on varying degrees of oxidation susceptibility of oil from different feedstock. The existing techniques are expensive and have limitations to determine the exact source of oil, especially when there is mixing. This article is designed to highlight a need for developing a technique that can be easily used to determine the source of oil or biodiesel based on carbon isotope ratio in different regions of the world. It would be like a litmus test to check the source of oil for biodiesel.

Technical Notes

The isotopes of an element are the various configurations of its atoms. There are three carbon isotopes in nature: 12C, 13C and 14C. Terrestrial vegetation and marine phytoplankton, in the process of photosynthetic absorption of CO2, preferably incorporate C12 instead of C13. But a specific amount of C13 is also incorporated based on photosynthetic carbon fixation mechanism of plants, and the ratio of incorporated carbon isotopes may provide an analytical clue to differentiate among oil/biodiesel from different plants.

The popularity of biodiesel may create some conflicts in the future while assessing the source of oil as edible or nonedible, and expected shelf life depending on varying degrees of oxidation susceptibility of oil from different feedstock. This study is proposed to develop a technique that can be used to differentiate the source of oil in biodiesel based on carbon isotope ratio. Samples of a variety of biodiesel feedstock can be analyzed for the presence of specific isotope ratio of carbon elements, which is considered to be different in different types of plants based on their carbon fixation mechanism and environment. Identification of the carbon isotopes can be performed by using continuous flow-isotope ratio mass spectrometry (CF-IRMS). Statistical methods can be applied to determine the relation of carbon isotope ratio to their specific origin of oils. The outcome of this study will be helpful not only to differentiate biodiesel from edible or nonedible feedstock, but it will also provide data about the exact origin of oil/biodiesel. The shelf life of the oils/biodiesel can also be predicted based on standard unsaturation in the specific feedstock. This study will facilitate the choice of biodiesel and eradicate the confusion of edible or nonedible or mixing of biodiesel from different origins. The proposed study is not reported before by any organization or researchers.

Almost 99 percent of atmospheric CO2 contains the less heavy carbon, C12. A small part, 1 percent of CO2, is somewhat heavier, since it contains 13C. Therefore a very small proportion of a type of CO2 that contains 14C is radioactive and unstable, and whose applications have typically been in paleochronology (Investigating Earth’s early history). Terrestrial vegetation and marine phytoplankton, in the process of photosynthetic absorption of CO2, discriminate against heavy molecules preferring 12C over 13C. In this way, the carbon trapped in continental flora contains a smaller proportion of 13C than the carbon in atmospheric CO2 (1).

Plants are usually categorized into C3 and C4 carbon fixation plants based on their specificity to construct first photosynthesized organic compounds containing 3 and 4 carbon atoms, respectively. C3 carbon fixation plants have lower values of C13 while C4 carbon fixation plants have higher values of C13. Ishida-Fujii K et al (2005) has published a report on successful identification of alcohols from different botanical and geographical origin by stable isotope analyses of C, H and O (2).

Microalgae, blue-green algae and some macroalgae have been categorized as C4 fixation plants and must present high values of C13 isotopes. In spite of C3 or C4 fixation, carbon isotope ratio is also found different in different species with the same fixation mechanism (2). 

Literature study reveals that maize oil purity can be analyzed based on carbon isotope ratio (3). As the plants using either the C3 or the C4 photosynthetic pathway show distinct ratios of natural carbon isotopes in their tissues, the same way carbon isotope ratios are transferred with little distortion to herbivores feeding on plants of either photosynthetic type. These features may also help scientists to identify the animal fat as a source of biodiesel (4). Some studies have led the scientists to develop a test regarding intake of synthetic testosterone by the athletes, which are based on ratio of carbon isotopes. It is further connected to the presence of types of isotopes in the plants of specific region. There is a definite ratio of carbon isotopes in the people of specific region based on plant contents of that region. Scientists are trying to find the difference in ratio that is created by the intake of synthetic testosterone. Plants are responsible to fix the CO2 depending on the available ratio and nature of types of plants (i.e., C3 and C4 carbon fixation in plants) (5). The same technique is in the stage of improvement, and new methods are being developed to detect the isotopes based ratio of carbon atoms (6). Synthetic alcohol from petrochemical sources has low C14 content as compared to alcohol produced as a result of fermentation using contemporary carbohydrates (7).

Based on the available techniques, here it is proposed that a database of carbon isotope ratio can be established in different regions to differentiate the source of oil in biodiesel based on carbon isotope ratio. This method may be more accurate and preferred over existing X-Ray diffraction studies and Gas Chromatography-Mass Spectrometry techniques. The findings of this study will help to establish a summarized assay for the identification of source of oils in biodiesel and other related products.

The methodology may involve the analysis of the carbon isotope ratio of the feedstock/oil from edible and nonedible sources and analysis by database designed using software calculations. An identification of the carbon isotopes will be performed by using continuous flow-isotope ratio mass spectrometry (CF-IRMS). Statistical calculations will be performed using the database designed as a result of estimation of different types of carbon isotopes in samples. The study can be carried out by focusing on the objectives encompassing sampling of variety of usual raw material for biodiesel, carbon isotope determination from different raw material and establishing relation of ratio of carbon isotopes of oil from different feedstock followed by calculations and modeling.

The success of this proposed research can be predicted based on the cited references proving that carbon isotope ratio is quite different in different plants. To determine the carbon isotope ratio is an established technique and can be performed successfully at laboratory scale. Carbon Isotope Ratio Mass Spectrometry, Gas Chromatography and Computer Programming/ Modeling would be the main Instruments/Techniques required for this study.


  1. 1.    Carbon-13. C3 and C4 plants,
  2. 2.     Ishida-Fujii K, Goto S, Uemura R, Yamada K, Sato M, Yoshida N Botanical and geographical origin identification of industrial ethanol by stable isotope analyses of C, H, and O. Biosci Biotechnol Biochem. 2005 Nov;69(11):2193-9
  3. 3.    Rossell, J. B. (1994), Stable Carbon Isotope Ratios in Establishing Maize Oil Purity. Fett/Lipid, 96: 304–308. doi: 10.1002/lipi.19940960806.
  4. 4.    Jarrad Prasifka & Kevin Heinz, The use of C3 and C4 plants to study natural enemy movement and ecology, and its application to pest management DOI:   10.1080/09670870410001731907)
  5. 5.    E Strahm, C Emery, M Saugy, J Dvorak, C Saudan. Detection of testosterone administration based on the carbon isotope ratio profiling of endogenous steroids: international reference populations of professional soccer players Br J Sports Med 2009;43:1041-1044 doi:10.1136/bjsm.2009.058669
  6. 6.    Aguilera, R., Becchi, M., Casabianca, H., Hatton, C. K., Catlin, D. H., Starcevic, B. and Pope, H. G. (1996), Improved method of detection of testosterone abuse by gas chromatography/combustion/isotope ratio mass spectrometry analysis of urinary steroids. Journal of Mass Spectrometry, 31: 169–176. doi: 10.1002/(SICI)1096-9888(199602)31:2<169::AID-JMS276>3.0.CO;2-I
  7. 7.    McWeeny, D. J. and Bates, M. L. (1980), Discrimination between synthetic and natural ethyl alcohol in spirits and fortified wines. International Journal of Food Science & Technology, 15: 407–412. doi: 10.1111/j.1365-2621.1980.tb00956.x


Author: Ehsan Ali

Associate Professor, Centre for Advance Studies in Energy,

National University of Sciences and Technology (Pakistan)



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